1. Field of the Invention
The present invention is related to implantable medication dosing devices, and, in particular, to such a dosing device which permits controlled injection of liquid from a reservoir into a patient.
2. Description of the Prior Art and Related Applications
Implantable dosing devices are known for use in diabetes therapy which inject insulin from a reservoir into the body in accordance with a defined dosing program. The pump portion of such devices is preferably implanted, and the operating or programming part is extracorporeally disposed. Communication between the implanted and the extracorporeally units ensues by telemetric remote control. Because the pump of the dosing device is a part of the implanted unit, an energy source for the pump in the form of a battery must also be implanted. To achieve an optimally long service life of the battery, an efficient energy utilization by the pump drive is of special significance. It is also important to monitor the quantity of liquid conveyed and injected by the pump because life-threatening conditions could otherwise occur.
U.S. Pat. No. 4,486,190 discloses a dosing device of the type described above wherein the pump operation is monitored by a flow resistor at the pump output, and a pressure sensor in the pump chamber. This embodiment is suitable for diaphragm pumps, and is somewhat technologically complicated. This device is not suitable for piston pumps because piston pumps operate based on an optimized relationship between piston capacity and dead space, and are capable of pumping gases with a relatively high conveying rate given differential pressures, which cannot be suitably monitored by the above structure.
Moreover, such piston pumps can still convey the liquid to be injected even though gas bubbles may be situated in the liquid. In fact, the presence of such gas bubbles in piston pumps is substantially unavoidable in practice. Such a piston pump is disclosed in European application No. 87112040.8, and in copending U. S. application Ser. No. 182,723 (Franetzki et al) filed Apr. 18, 1988 now U.S. Pat. No. 4,883,467. In the pump of the latter application, structure has been disclosed to minimize formation and conveyance of such bubbles.
A further monitoring arrangement for an implantable piston pump in a medication dosing device is described in Austrian Patent No. 378 123. In the structure described therein, the noise generated by the normal operation of the drive coils of the piston of the piston pump is monitored by a noise sensor (microphone), and an alarm signal is triggered in the absence of such noise. It is not possible in this system to monitor the pump for functional deviations from rated values or to provide control instructions in the event of such deviations.
Another monitoring arrangement for an implanted infusion pump of a medication dosing device is described in European application No. 0 048 423. In this structure, electrically operating pulses ar wirelessly supplied to the pump drive, and an answerback is provided also wirelessly, to an externally disposed control unit or programming device and the reception of these pulses is confirmed. It is not possible in this system, however, to confirm whether the transmitted pulses have actually resulted in a pump motion which conveys the desired quantity of medication.
Another pump monitoring device in a pump for compressing ethylene gas is described in German No. OS 2 916 490, In this monitoring system, the function of the valves is monitored by obtaining, with an oscillatory pick-up, sound waves transmitted by the pump operation to the cylinder head, and comparing the signals received in this manner to rated values. An alarm or shut-off signal is triggered given recognization of a malfunction.